Modified polyimide and curable resin composition

ABSTRACT

The present invention relates to a modified polyimide including a terminal group represented by Formula 1: 
     
       
         
         
             
             
         
       
         
         
           
             wherein D is a heat curable or photocurable functional group, R is a divalent or higher polyvalent organic group, and n is an integer of 1 or greater. The modified polyimide undergoes less reduction in transmittance and is protected from discoloration when cured. Due to these advantages, the modified polyimide can provide a highly transparent colorless polyimide film. Particularly, the modified polyimide is suitable for use in display substrates, interlayer insulating films of semiconductor devices, passivation films, buffer coat films, insulating films for multilayer printed circuit boards, insulating films of OLEDs, and protective films of thin film transistors of liquid crystal display devices. The present invention also relates to a curable composition including the modified polyimide.

This application claims the benefit of priority to Korean PatentApplication No. 10-2015-0130041, filed on Sep. 15, 2015, the entiredisclosure of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a modified polyimide and a curableresin composition. More specifically, the present invention relates to acurable resin composition for the production of a more colorlesstransparent polyimide film.

2. Description of the Related Art

Organic films have the advantages of higher bendability, lessbrittleness, and lighter weight than glass. With the recent trendtowards flexible displays, substrates for flat panel displays have beenreplaced with organic films.

Transparent polymer plastics are advantageous in terms of ease ofprocessing, mass productivity, and price. Due to these advantages,transparent polymer plastics are widely used at present as materials forcover windows and touch panels for the protection of windows of flatpanel display devices.

Like films for displays, films for touch panel substrates are alsooptical components for better visibility of LCD and OLED screens and arethus required to have low haze and high transmittance. Further, filmsfor touch panel substrates should be highly durable under variousenvironmental conditions as well as against fingernails due to thefrequent finger touch. For high durability, transparent polymer plasticsneed surface treatment with high-hardness hard coating. High surfacehardness, impact resistance, and flex resistance are requirements forthe manufacture of high hardness products. PET or cyclo-olefin polymer(COP) films are currently in use for touch panel substrates. However,high retardation of PET causes diffuse reflection of incident light,making screen images invisible. High deposition temperature is requiredto lower the resistance of ITO in touch panels. However, the depositiontemperatures of some COP substrate films are difficult to increase dueto their poor heat resistance. That is, there are no materials that cansimultaneously meet three requirements: excellent heat resistance,optical properties, and mechanical properties for high processability.

In recent years, polymethyl methacrylate (PMMA) resin sheets have beenused for outer windows of portable display devices in place oftransparent glass substrates. Due to their poor impact resistance,however, PMMA resin sheets tend to be brittle even when small externalimpacts are applied thereto. Some transparent sheets for outer windowsof potable display devices are produced by coextrusion of a PMMA resinwith a polycarbonate (PC) resin. The polycarbonate (PC) resin impartsimpact resistance to the transparent sheets. However, the outer windowsare pushed back when pushed down with a finger because of relatively lowflexural modulus of the sheets.

On the other hand, cyclo-olefin polymer (COP) films exhibit excellentcharacteristics in terms of transparency, hygroscopicity, etc., but theyhave relatively low flexibility, heat resistance, and surface hardness.Particularly, relatively low surface hardness of cyclo-olefin polymer(COP) films leads to low scratch resistance. That is, cyclo-olefinpolymer (COP) films are not sufficiently protected from scratches.

In attempts to solve such problems, many methods have been developed forproducing flexible films in which transparent resin layers with goodheat resistance and high strength are laminated. However, the laminationof multiple resin layers is inefficient in terms of processing andproblems may arise from poor adhesion between the resin layers.

Some processes, such as evaporation deposition and sputtering, areessential for the production of transparent electrodes. Since suchprocesses are carried out at high temperatures of at least 200° C., heatresistance of flexible substrates is considered an important factor inthe production of transparent electrodes. Fillers may be added tomaintain the basic mechanical properties (e.g., heat resistance) offlexible substrates. In this case, however, voids may be formed on thesurface of substrates, resulting in poor hygroscopicity. Particularly,high dielectric constant fillers are used to improve the heat resistanceof substrates but may deteriorate the adhesion of substrates to copperfoils. When polymeric materials containing fillers are used forsubstrates, the substrate materials lose their flexibility, tending tobe brittle. A method for improving the strength, heat resistance, andadhesiveness of a substrate is known in which a glass fiber is used tomake a polymeric material into a prepreg. However, this method isdifficult to use in applications where high dielectric constant isneeded because the polymeric material loses its dielectric constant.

Hard coating agents are coated on substrates, dried, and UV cured toform hard coatings. Such hard coating agents include a polyfunctionalacrylic oligomer, a polyfunctional acrylic monomer, a photoinitiator,and a solvent. However, most hard coating agents suffer from thedisadvantages of poor flex resistance and impact resistance when it isintended to increase the crosslinking density of coatings for betterhardness. The use of high molecular weight acrylic oligomers or flexibleacrylate oligomers and monomers including ethylene oxide in theirmolecules contributes to improvements in the flex resistance and impactresistance of substrates but leads to low hardness.

Particularly, fluorine compounds and silicon compounds are mainly usedto improve the scratch resistance and fouling resistance of films.Fluorine-containing polymers with low refractive index andfluorine-containing olefin copolymers exhibit extremely high water andoil repellency and expose —CF₂— or —CF₃ groups at the surface of filmsto ensure good antifouling properties, but are not readily formed intofilms by coating because they are hardly soluble in solvents. Thesepolymers and copolymers are very expensive and undergo drastic changesin physical properties depending on molding conditions.

In addition to good heat resistance, polyimide resins have outstandingmechanical properties, including mechanical strength, wear resistance,dimensional stability, and chemical resistance, and excellent electricalproperties, including insulation performance. Due to these advantages,polyimide resins are used in a wide range of industrial applications,including electrical and electronic applications.

Polyimides are widely used as highly heat resistant advanced materials,such as automotive materials and aeronautical materials, and in thefield of electronic devices, such as interlayer insulating films forsemiconductors, buffer coats, substrates for flexible printed circuitboards, liquid crystal alignment layers, and electrical insulatingmaterials, because of their excellent mechanical properties, heatresistance, chemical resistance, and electrical insulation properties.

However, general polyimide resins have high transmittance in the visibleregion owing to their high density aromatic cyclic structure and arecolored yellowish owing to their very low transmittance, particularly atwavelengths of around 400 nm, limiting their use in applications wheretransparency is required.

Colorless transparent polyimide resins can be used as raw materials forthe production of highly heat resistant transparent coatings and filmsin the field of electronic devices, for example, materials for electrodeinsulating films and transparent protective films in the field of liquidcrystal displays, hard coating films of touch panels, and hard coatingfilms and transparent films in transparent flexible substrates.

Under these circumstances, continued efforts have been made to developpolyimides that can exhibit better chemical resistance and storagestability, sufficient mechanical properties, and excellent hightemperature stability.

SUMMARY OF THE INVENTION

One object of the present invention is to provide a modified polyimideincluding curable functional groups.

A further object of the present invention is to provide a curable resincomposition including the modified polyimide.

Another object of the present invention is to provide a modifiedpolyimide film produced using the curable resin composition.

Still another object of the present invention is to provide a method forpreparing the modified polyimide.

One aspect of the present invention provides a modified polyimideincluding a terminal group represented by Formula 1:

wherein D is a heat curable or photocurable functional group, R is adivalent or higher polyvalent organic group, and n is an integer of 1 orgreater.

The terminal group of Formula 1 may be derived from the reaction of aterminal acid dianhydride group of a polyimide and a compound of Formula2:

O═C═N—RD]_(n)  (2)

wherein R, D, and n are as defined in Formula 1.

The modified polyimide may be represented by Formula 4:

wherein D, R, and n are as defined above, X₁, X₂, X₃, and X₄ are eachindependently a tetravalent organic group derived from a tetracarboxylicdianhydride, Y₁, Y₂, and Y₃ are each independently a divalent organicgroup derived from a diamine, and p, q, r, and v are each independentlyan integer of 0 or greater, with the proviso that p, q, r, and v are notsimultaneously 0.

The modified polyimide may further include, in its main chain, one ormore repeating structures represented by Formulae 5a to 5c:

wherein R_(a) and R_(b) are each independently selected from the groupconsisting of aromatic, alicyclic, and aliphatic divalent organicgroups,

wherein R_(c) and R_(d) are each independently selected from the groupconsisting of aromatic, alicyclic, and aliphatic divalent organicgroups, and

wherein R_(e) and R_(f) are each independently selected from the groupconsisting of aromatic, alicyclic, and aliphatic divalent organicgroups.

D in Formula 1 may be selected from the group consisting of vinyl,alkyne, acrylate, carboxyl, amide, amino, epoxy, isocyanate, cyano, acidanhydride, mercapto, silanol, alkoxysilane, hydroxyl, oxazoline groups,and combinations thereof. More specifically, D in Formula 1 may beselected from acrylate, epoxy, isocyanate, and mercapto groups.

In Formula 4, X₁, X₂, X₃, and X₄ may be each independently a tetravalentorganic group derived from an aromatic tetracarboxylic dianhydride andY₁, Y₂, and Y₃ may be each independently a divalent organic groupderived from an aromatic diamine.

The modified polyimide of Formula 4 may be prepared by reacting apolyimide compound having terminal acid dianhydride groups, representedby Formula 3:

wherein X₁, X₂, X₃, and X₄ are each independently a tetravalent organicgroup derived from a tetracarboxylic dianhydride, Y₁, Y₂, and Y₃ areeach independently a divalent organic group derived from a diamine, andw and z are each independently an integer of 1 or greater, with anisocyanate compound represented by Formula 2:

O═C═N—RD]_(n)  (2)

wherein D is a heat curable or photocurable functional group, R is adivalent or higher polyvalent organic group, n is an integer of 1 orgreater.

The modified polyimide may have a number average molecular weight of 500to 80,000 g/mol.

In Formula 4, the sum of p+q+r+v may be an integer from 5 to 100.

The ratio of the weight average molecular weight to the number averagemolecular weight of the modified polyimide may be 1 or greater.

The isocyanate compound of Formula 2 may be a compound represented byFormula 2a:

wherein R₁ is a C₁-C₁₈ alkylene group, an arylene group or a divalentorganic group interrupted by at least one ether, ester, urethane, amide,siloxane or silazane bond, in which at least one hydrogen atom isoptionally substituted with a substituent selected from the groupconsisting of halogen atoms, C₁-C₁₀ alkyl groups, halogenated alkylgroups, C₃-C₃₀ cycloalkyl groups, C₆-C₃₀ aryl groups, a hydroxyl group,C₁-C₁₀ alkoxy groups, a carboxylic acid group, an aldehyde group, anepoxy group, a cyano group, a nitro group, an amino group, a sulfonicacid group, and derivatives thereof, and R₂ is a hydrogen atom or aC₁-C₁₈ alkyl group.

The polyimide of Formula 3 may be prepared by reacting thetetracarboxylic dianhydride with the diamine in a molar ratio of 1:1 to1.8:1.

A further aspect of the present invention provides a curable resincomposition including the modified polyimide, a thermal polymerizationor photopolymerization initiator, and a solvent.

The solvent may be selected from N,N-diethylacetamide (DEAc),N,N-diethylformamide (DEF), N-ethylpyrrolidone, and mixtures thereof.

The curable resin composition may further include a polymerizablecompound having an ethylenically unsaturated bond, a urethane(meth)acrylate compound or a mixture thereof.

Another aspect of the present invention provides a polyimide filmproduced using the curable resin composition.

According to one embodiment, the polyimide film may have a yellownessindex (YI) of 7 or less, as measured at a thickness of 10 μm or more.

Yet another aspect of the present invention provides a method forpreparing a modified polyimide having terminal curable functionalgroups, represented by Formula 4:

wherein X₁, X₂, X₃, and X₄ are each independently a tetravalent organicgroup derived from a tetracarboxylic dianhydride, Y₁, Y₂, and Y₃ areeach independently a divalent organic group derived from a diamine, p,q, r, and v are each independently an integer of 0 or greater, with theproviso that p, q, r, and v are not simultaneously 0, D is a heatcurable or photocurable functional group, R is a divalent or higherpolyvalent organic group, and n is an integer of 1 or greater, themethod including reacting the tetracarboxylic dianhydride with thediamine in a polymerization solvent to prepare a polyamic acid,imidizing the polyamic acid to prepare a polyimide having terminal aciddianhydride groups, represented by Formula 3:

wherein X₁, X₂, X₃, X₄, Y₁, Y₂, and Y₃ are as defined above and w and zare each independently an integer of 1 or greater, and reacting thepolyimide of Formula 3 with a compound represented by Formula 2:

O═C═N—RD]_(n)  (2)

wherein D, R, and n are as defined above.

According to one embodiment, the polymerization solvent may be selectedfrom methyl ethyl ketone, cyclohexanone, toluene, xylene,tetramethylbenzene, ethylene glycol monoethyl ether, ethylene glycolmonomethyl ether, ethylene glycol monobutyl ether, diethylene glycolmonoethyl ether, diethylene glycol monomethyl ether, diethylene glycolmonobutyl ether, propylene glycol monomethyl ether, propylene glycolmonoethyl ether, dipropylene glycol diethyl ether, triethylene glycolmonoethyl ether, ethyl acetate, butyl acetate, ethylene glycol monoethylether acetate, ethylene glycol monobutyl ether acetate, diethyleneglycol monoethyl ether acetate, dipropylene glycol monomethyl etheracetate, ethanol, propanol, ethylene glycol, propylene glycol, carbitol,dimethylacetamide (DMAc), N,N-diethylacetamide, dimethylformamide (DMF),diethylformamide (DEF), N,N-dimethylacetamide (DMAc),N-methylpyrrolidone (NMP), N-ethylpyrrolidone (NEP),1,3-dimethyl-2-imidazolidinone, N, N-dimethylmethoxyacetamide, dimethylsulfoxide, pyridine, dimethyl sulfone, hexamethylphosphoramide,tetramethylurea, N-methylcaprolactam, tetrahydrofuran, m-dioxane,p-dioxane, 1,2-dimethoxyethane, bis(2-methoxyethyl)ether,1,2-bis(2-methoxyethoxy)ethane, bis[2-(2-methoxyethoxy)]ether, andmixtures thereof.

Details of other embodiments of the present invention are included inthe detailed description that follows.

The modified polyimide of the present invention has terminal heatcurable or photocurable functional groups in the main chain. Thisstructure allows faster curing of a curable resin composition includingthe modified polyimide and enables the production of a more colorlesstransparent polyimide film.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows attenuated total reflectance (ATR) spectra of polyimidesprepared in Preparative Examples 2 and 3.

FIG. 2 shows ATR spectra of polyimides prepared in Preparative Examples1 and 2 from which ATR peaks of a polyimide prepared in PreparativeExample 3 are excluded.

FIG. 3 shows HMBC NMR (¹H-¹³C) and COSY NMR (¹H-¹H) spectra of apolyimide prepared in Preparative Example 5.

FIG. 4 shows ¹H-NMR spectra of polyimides prepared in PreparativeExamples 1, 2, 5, and 6 and imidization ratios of the polyimidescalculated from the spectra.

FIG. 5 shows ¹H-NMR spectra of polyimides prepared in PreparativeExamples 5, 7, and 8.

DETAILED DESCRIPTION OF THE INVENTION

As the present invention allows for various changes and numerousembodiments, particular embodiments will be illustrated in drawings anddescribed in detail in the written description. However, this is notintended to limit the present invention to particular modes of practice,and it is to be appreciated that all changes, equivalents, andsubstitutes that do not depart from the spirit and technical scope ofthe present invention are encompassed in the present invention. In thedescription of the present invention, detailed explanations of relatedart are omitted when it is deemed that they may unnecessarily obscurethe essence of the present invention.

Unless otherwise stated, all compounds or functional groups may besubstituted or unsubstituted. The term “substituted” used herein meansthat at least one of the hydrogen atoms contained in the compounds orfunctional groups is replaced by a substituent selected from the groupconsisting of halogen atoms, C₁-C₁₀ alkyl groups, halogenated alkylgroups, C₃-C₃₀ cycloalkyl groups, C₆-C₃₀ aryl groups, a hydroxyl group,C₁-C₁₀ alkoxy groups, a carboxylic acid group, an aldehyde group, anepoxy group, a cyano group, a nitro group, an amino group, a sulfonicacid group, and derivatives thereof.

Unless otherwise mentioned, the term “combination thereof” means thattwo or more functional groups are bonded to each other via a linkinggroup, such as a single bond, a double bond, a triple bond, a C₁-C₁₀alkylene group (e.g., a methylene (—CH₂—) or ethylene (—CH₂CH₂—) group),a C₁-C₁₀ fluoroalkylene group (e.g., a fluoromethylene (—CF₂—) orperfluoroethylene (—CF₂CF₂—) group), a heteroatom, such as N, O, P, S orSi, or a functional group containing the heteroatom (specifically, aheteroalkylene group containing a carbonyl (—C═O—) group, an ether (—O—)group, an ester (—COO—) group, —S—, —NH— or —N═N— in the molecule), ortwo or more functional groups are fused together.

The present invention provides a modified polyimide including a terminalgroup represented by Formula 1:

wherein D is a heat curable or photocurable functional group, R is adivalent or higher polyvalent organic group, and n is an integer of 1 orgreater.

The present invention also provides a curable resin compositionincluding the modified polyimide.

The present invention also provides a polyimide film produced using thecurable resin composition.

The present invention also provides a method for preparing the modifiedpolyimide.

The functional group of Formula 1 may be a heat curable or photocurablefunctional group derived from the reaction of a terminal aciddianhydride group of a polyimide and a compound of Formula 2:

O═C═N—RD]_(n)  (2)

wherein R, D, and n are as defined in Formula 1.

The heat curable or photocurable functional group D may be selected fromthe group consisting of vinyl, alkyne, acrylate, carboxyl, amide, amino,epoxy, isocyanate, cyano, acid anhydride, mercapto, silanol,alkoxysilane, hydroxyl, oxazoline groups, and combinations thereof.Preferably, D is selected from acrylate, epoxy, isocyanate, and mercaptogroups. More preferably, D is an acrylate group.

More specifically, the compound of Formula 2 may be selected fromcompounds represented by Formulae 2a to 2c:

wherein R₁ is a C₁-C₁₈ alkylene group, a C₆-C₂₄ arylene group or adivalent organic group interrupted by at least one ether, ester,urethane, amide, siloxane or silazane bond, in which at least onehydrogen atom is optionally substituted with a substituent selected fromthe group consisting of halogen atoms, C₁-C₁₀ alkyl groups, halogenatedalkyl groups, C₃-C₃₀ cycloalkyl groups, C₆-C₃₀ aryl groups, a hydroxylgroup, C₁-C₁₀ alkoxy groups, a carboxylic acid group, an aldehyde group,an epoxy group, a cyano group, a nitro group, an amino group, a sulfonicacid group, and derivatives thereof, preferably a halogen atom, a C₁-C₁₀alkyl group or a halogenated alkyl group, and R₂ is a hydrogen atom or aC₁-C₁₈ alkyl group,

wherein R₃ is a C₁-C₁₈ alkylene group, a C₆-C₂₄ arylene group or adivalent organic group interrupted by at least one ether, ester,urethane, amide, siloxane or silazane bond, in which at least onehydrogen atom is optionally substituted with a substituent selected fromthe group consisting of halogen atoms, C₁-C₁₀ alkyl groups, halogenatedalkyl groups, C₃-C₃₀ cycloalkyl groups, C₆-C₃₀ aryl groups, a hydroxylgroup, C₁-C₁₀ alkoxy groups, a carboxylic acid group, an aldehyde group,an epoxy group, a cyano group, a nitro group, an amino group, a sulfonicacid group, and derivatives thereof, preferably a halogen atom, a C₁-C₁₀alkyl group or a halogenated alkyl group, and R₄ is a hydrogen atom or aC₁-C₁₈ alkyl group, and

O═C═N—R₅—SH  (2c)

wherein R₅ is a C₁-C₁₈ alkylene group, a C₆-C₂₄ arylene group or adivalent organic group interrupted by at least one ether, ester,urethane, amide, siloxane or silazane bond, in which at least onehydrogen atom is optionally substituted with a substituent selected fromthe group consisting of halogen atoms, C₁-C₁₀ alkyl groups, halogenatedalkyl groups, C₃-C₃₀ cycloalkyl groups, C₆-C₃₀ aryl groups, a hydroxylgroup, C₁-C₁₀ alkoxy groups, a carboxylic acid group, an aldehyde group,an epoxy group, a cyano group, a nitro group, an amino group, a sulfonicacid group, and derivatives thereof, preferably a halogen atom, a C₁-C₁₀alkyl group or a halogenated alkyl group.

Preferred is the compound of Formula 2a modified with an acryloyl groupand an isocyanate group.

The present invention provides a method for preparing a modifiedpolyimide having terminal curable functional groups, represented byFormula 4:

wherein D is a heat curable or photocurable functional group, R is adivalent or higher polyvalent organic group, n is an integer of 1 orgreater, X₁, X₂, X₃, and X₄ are each independently a tetravalent organicgroup derived from a tetracarboxylic dianhydride, Y₁, Y₂, and Y₃ areeach independently a divalent organic group derived from a diamine, andp, q, r, and v are each independently an integer of 0 or greater, withthe proviso that p, q, r, and v are not simultaneously 0, the methodincluding reacting the tetracarboxylic dianhydride with the diamine in apolymerization solvent to prepare a polyamic acid, imidizing thepolyamic acid to prepare a polyimide having terminal acid dianhydridegroups, represented by Formula 3:

wherein X₁, X₂, X₃, X₄, Y₁, Y₂, and Y₃ are as defined above and w and zare each independently an integer of 1 or greater, with the proviso thatthe sum of w+z is greater than or equal to the sum of p+q+r+v, andreacting the polyimide of Formula 3 with a compound represented byFormula 2:

O═C═N—RD]_(n)  (2)

wherein D, R, and n are as defined above.

In Formula 4, the sum of p+q+r+v may be an integer from 2 to 100.

According to the method of the present invention, the isocyanate groupof the compound of Formula 2 reacts with the terminal dianhydride groupsof the polyimide and the imide groups present in the main chain of thepolyimide to ring open the imide groups. As a result, the organic grouphaving the terminal curable functional group is bonded to the sidechains of the ring-opened polyimide.

The polyimide of the present invention may further include, in its mainchain, one or more repeating structures represented by Formulae 5a to5c:

wherein R_(a) and R_(b) are each independently selected from the groupconsisting of aromatic, alicyclic, and aliphatic divalent organicgroups,

wherein R_(c) and R_(d) are each independently selected from the groupconsisting of aromatic, alicyclic, and aliphatic divalent organicgroups, and

wherein R_(e) and R_(f) are each independently selected from the groupconsisting of aromatic, alicyclic, and aliphatic divalent organicgroups.

Specifically, R_(a), R_(b), R_(c), R_(d), R_(e), and R_(f) in Formulae5a to 5c may be divalent aromatic organic groups represented by Formulae9a to 9d. More specifically, R_(a), R_(b), R_(c), R_(d), R_(e), andR_(f) in Formulae 5a to 5c may be divalent aromatic organic groupsrepresented by Formulae 10a to 10q. Formulae 9a to 9d and 10a to 10q areprovided below.

X₁, X₂, X₃, and X₄ in Formula 4 may be each independently a tetravalentorganic group derived from a dianhydride. More preferably, X₁, X₂, X₃,and X₄ in Formula 4 is each independently derived from a tetracarboxylicdianhydride including a tetravalent aromatic organic group.

Tetracarboxylic dianhydrides suitable for use in the preparation of thepolyimide of Formula 3 may be those including the functional groups X₁,X₂, X₃, and X₄ in Formula 3 and may be, for example, those including atetravalent organic group in which monocyclic aromatic groups,polycyclic aromatic groups or combinations thereof are linked to eachother through crosslinking structures in the molecule.

X₁, X₂, X₃, and X₄ in Formula 4 may be selected from the groupconsisting of tetravalent aromatic organic groups represented byFormulae 7a to 7d:

wherein R₁₁ is a C₁-C₁₀ alkyl or C₁-C₁₀ fluoroalkyl group and a2 is aninteger of 0 or 2,

wherein R₁₂ is a C₁-C₁₀ alkyl or C₁-C₁₀ fluoroalkyl group and b2 is aninteger of 0 to 4,

wherein R₁₃ is a C₁-C₁₀ alkyl or C₁-C₁₀ fluoroalkyl group and c2 is aninteger of 0 to 8, and

wherein R₁₄ and R₁₅ are each independently a C₁-C₁₀ alkyl or C₁-C₁₀fluoroalkyl group, d2 and e2 are each independently an integer of 0 to3, f2 is an integer of 0 to 3, and A₁₁ is selected from the groupconsisting of a single bond, —O—, —CR₁₈R₁₉—, —C(═O)—, —C(═O)NH—, —S—,—SO₂—, a phenylene group, and combinations thereof (where R₁₈ and R₁₉are each independently selected from the group consisting of a hydrogenatom, C₁-C₁₀ alkyl groups, and C₁-C₁₀ fluoroalkyl groups).

More specifically, X₁, X₂, X₃, and X₄ in Formula 3 may be selected from,but not limited, those represented by Formulae 8a to 8l:

wherein A₂ is selected from the group consisting of a single bond, —O—,—C(═O)—, —C(═O)NH—, —S—, —SO₂—, a phenylene group, and combinationsthereof and v is an integer of 0 or 1.

At least one hydrogen atom present in each of the tetravalent aromaticorganic groups of Formulae 8a to 8l may also be substituted with aC₁-C₁₀ alkyl group (e.g., a methyl, ethyl, propyl, isopropyl, t-butyl,pentyl or hexyl group) or a C₁-C₁₀ fluoroalkyl group (e.g., afluoromethyl, perfluoroethyl or trifluoromethyl group).

Diamines suitable for use in the preparation of the polyimide of Formula3 may be diamine compounds including the divalent organic groups Y₁, Y₂,and Y₃.

Specifically, Y₁, Y₂, and Y₃ in Formula 3 are divalent aromatic organicgroups derived from aromatic diamine compounds or combinations thereofand may be aliphatic, alicyclic or aromatic divalent organic groupslinked directly to each other or divalent organic groups linked to eachother through a crosslinking structure. More specifically, Y₁, Y₂, andY₃ in Formula 3 may be selected from the group consisting of functionalgroups represented by Formulae 9a to 9d:

wherein R₅₁ is selected from the group consisting of C₁-C₁₀ alkyl groups(e.g., methyl, ethyl, propyl, isopropyl, t-butyl, pentyl, and hexylgroups), C₁-C₁₀ fluoroalkyl groups (e.g., fluoromethyl, perfluoroethyl,and trifluoromethyl groups), C₆-C₁₂ aryl groups (e.g., phenyl andnaphthalenyl groups), a sulfonic acid croup, and a carboxylic acid croupand a3 is an integer of 0 to 4,

wherein R₅₂ is selected from the group consisting of C₁-C₁₀ alkyl groups(e.g., methyl, ethyl, propyl, isopropyl, t-butyl, pentyl, and hexylgroups), C₁-C₁₀ fluoroalkyl groups (e.g., fluoromethyl, perfluoroethyl,and trifluoromethyl groups), C₆-C₁₂ aryl groups (e.g., phenyl andnaphthalenyl groups), a sulfonic acid group, and a carboxylic acid groupand b3 is an integer of 0 to 6,

wherein R₅₃ is selected from the group consisting of C₁-C₁₀ alkyl groups(e.g., methyl, ethyl, propyl, isopropyl, t-butyl, pentyl, and hexylgroups), C₁-C₁₀ fluoroalkyl groups (e.g., fluoromethyl, perfluoroethyl,and trifluoromethyl groups), C₆-C₁₂ aryl groups (e.g., phenyl andnaphthalenyl groups), a sulfonic acid group, and a carboxylic acid croupand c3 is an integer of 0 to 3, and

wherein R₅₄ and R₅₅ are each independently selected from the groupconsisting of C₁-C₁₀ alkyl groups (e.g., methyl, ethyl, propyl,isopropyl, t-butyl, pentyl, and hexyl groups), C₁-C₁₀ fluoroalkyl groups(e.g., fluoromethyl, perfluoroethyl, and trifluoromethyl groups), C₆-C₁₂aryl groups (e.g., phenyl and naphthalenyl groups), a sulfonic acidgroup, and a carboxylic acid group, d3 and e3 are each independently aninteger of 0 to 4, and A₂₁ is selected from the group consisting of asingle bond, —O—, —CR₅₆R₅₇—, —C(═O)—, —C(═O)NH—, —S—, —SO₂—, a phenylenegroup, and combinations thereof (where R₅₆ and R₅₇ are eachindependently selected from the group consisting of a hydrogen atom,C₁-C₁₀ alkyl groups (e.g., methyl, ethyl, propyl, isopropyl, t-butyl,pentyl, and hexyl groups), and C₁-C₁₀ fluoroalkyl groups (e.g.,fluoromethyl, perfluoroethyl, and trifluoromethyl groups).

Y₁, Y₂, and Y₃ in Formula 3 may be combinations of the functional groupsof Formulae 9a to 9d.

The presence of amino groups at the para-position means the location ofthe amino groups at the 1- and 4-positions of a single benzene ring butis not limited to this location. For a fused benzene ring or a structureof benzene rings linked via a linking group, the presence of aminogroups at the para-position means that the amino groups are substitutedat the most distant positions from each other.

More specifically, the divalent organic group including amino groups atthe para-position may be selected from the group consisting offunctional groups represented by Formulae 10a to 10q:

wherein A₂ is selected from the group consisting of a single bond, —O—,—CR₅₆R₅₇—, —C(═O)—, —C(═O)NH—, —S—, —SO₂—, a phenylene group, andcombinations thereof (where R₅₆ and R₅₇ are each independently selectedfrom the group consisting of a hydrogen atom, C₁-C₁₀ alkyl groups (e.g.,methyl, ethyl, propyl, isopropyl, t-butyl, pentyl, and hexyl groups),and C₁-C₁₀ fluoroalkyl groups (e.g., fluoromethyl, perfluoroethyl, andtrifluoromethyl groups)), and v is an integer of 0 or 1.

One or more hydrogen atoms in each of the divalent functional groups ofFormulae 10a to 10q may also be substituted with substituents selectedfrom the group consisting of C₁-C₁₀ alkyl groups (e.g., methyl, ethyl,propyl, isopropyl, t-butyl, pentyl, and hexyl groups), C₁-C₁₀fluoroalkyl groups (e.g., fluoromethyl, perfluoroethyl, andtrifluoromethyl groups), C₆-C₁₂ aryl groups (e.g., phenyl andnaphthalenyl groups), a sulfonic acid group, and a carboxylic acidgroup.

The polyimide of Formula 3 may be prepared by polymerization of thetetracarboxylic dianhydride and the diamine compound. The polymerizationreaction may be carried out by any suitable polymerization process, suchas solution polymerization, for the preparation of polyimides orprecursors thereof.

Specifically, according to solution polymerization, the diamine compoundis dissolved in a polymerization solvent and the acid dianhydride isadded to the solution to react with the diamine compound.

It is preferred to react the acid dianhydride with the diamine compoundin an appropriate ratio taking into consideration the physicalproperties of the final polyimide. Specifically, the diamine compound isreacted with the acid dianhydride in a molar ratio of about 1:1.8,preferably 1:1.1 to 1:1.5, more preferably 1:1.1 to 1:1.3. That is, thepolyimide having terminal dianhydride groups is prepared by reacting theexcess acid dianhydride with the diamine.

Specifically, the polymerization solvent is an organic solvent selectedfrom the group consisting of ketones, such as methyl ethyl ketone andcyclohexanone, aromatic hydrocarbons, such as toluene, xylene, andtetramethylbenzene, glycol ethers (cellosolves), such as ethylene glycolmonoethyl ether, ethylene glycol monomethyl ether, ethylene glycolmonobutyl ether, diethylene glycol monoethyl ether, diethylene glycolmonomethyl ether, diethylene glycol monobutyl ether, propylene glycolmonomethyl ether, propylene glycol monoethyl ether, dipropylene glycoldiethyl ether, and triethylene glycol monoethyl ether, ethyl acetate,butyl acetate, ethylene glycol monoethyl ether acetate, ethylene glycolmonobutyl ether acetate, diethylene glycol monoethyl ether acetate,dipropylene glycol monomethyl ether acetate, ethanol, propanol, ethyleneglycol, propylene glycol, carbitol, dimethylacetamide (DMAc),N,N-diethylacetamide, dimethylformamide (DMF), diethylformamide (DEF),N,N-dimethylacetamide (DMAc), N-methylpyrrolidone (NMP),N-ethylpyrrolidone (NEP), 1,3-dimethyl-2-imidazolidinone,N,N-dimethylmethoxyacetamide, dimethyl sulfoxide, pyridine, dimethylsulfone, hexamethylphosphoramide, tetramethylurea, N-methylcaprolactam,tetrahydrofuran, m-dioxane, p-dioxane, 1,2-dimethoxyethane,bis(2-methoxyethyl)ether, 1,2-bis(2-methoxyethoxy)ethane,bis[2-(2-methoxyethoxy)]ether, and mixtures thereof. Preferably, thepolymerization solvent is N,N-diethylacetamide, N,N-diethylformamide,N-ethylpyrrolidone or a mixture thereof.

The polymerization reaction is preferably carried out at a temperatureof about 30 to about 65° C. or about 40 to about 60° C. for about 5 toabout 50 hours, about 10 to about 40 or about 20 to about 30 hours afterstirring at a temperature of about 10 to less than about 30° C., at atemperature of about 15 to about 25° C. or at room temperature for about0.5 to about 5 hours or about 1 to about 3 hours.

When the polyamic acid or the polyimide is synthesized, excess polyaminogroups or acid anhydride groups need to be inactivated. To this end, adicarboxylic anhydride or a monoamine may be further added as anend-capping agent to cap the ends of the polyimide. The polyimide ispreferably end-capped with a dicarboxylic anhydride.

Examples of dicarboxylic anhydrides suitable for end-capping thepolyimide or the polyamic acid include phthalic anhydride,2,3-benzophenonedicarboxylic anhydride, 3,4-benzophenonedicarboxylicanhydride, 2,3-dicarboxyphenyl phenyl ether anhydride,2,3-biphenyldicarboxylic anhydride, 3,4-biphenyldicarboxylic anhydride,2,3-dicarboxyphenyl phenyl sulfone anhydride, 3,4-dicarboxyphenyl phenylsulfone anhydride, 2,3-dicarboxyphenyl phenyl sulfide anhydride,1,2-naphthalenedicarboxylic anhydride, 2,3-naphthalenedicarboxylicanhydride, 1,8-naphthalenedicarboxylic anhydride,1,2-anthracenedicarboxylic anhydride, 2,3-anthracenedicarboxylicanhydride, and 1,9-anthracenedicarboxylic anhydride. These dicarboxylicanhydrides may have a group unreactive with amines or dicarboxylicanhydrides in their molecules.

Examples of monoamines suitable for end-capping the polyimide or thepolyamic acid include aniline, o-toluidine, m-toluidine, p-toluidine,2,3-xylidine, 2,4-xylidine, 2,5-xylidine, 2,6-xylidine, 3,4-xylidine,3,5-xylidine, o-chloroaniline, m-chloroaniline, p-chloroaniline,o-bromoaniline, m-bromoaniline, p-bromoaniline, o-nitroaniline,m-nitroaniline, p-nitroaniline, o-aminophenol, m-aminophenol,p-aminophenol, o-anisidine, m-anisidine, p-anisidine, o-phenetidine,m-phenetidine, p-phenetidine, o-aminobenzaldehyde, m-aminobenzaldehyde,p-aminobenzaldehyde, o-aminobenzonitrile, m-aminobenzonitrile,p-aminobenzonitrile, 2-aminobiphenyl, 3-aminobiphenyl, 4-aminobiphenyl,2-aminophenyl phenyl ether, 3-aminophenyl phenyl ether, 4-aminophnylphenyl ether, 2-aminobenzophenone, 3-aminobenzophenone,4-aminobenzophenone, 2-aminophenyl phenyl sulfide, 3-aminophenyl phenylsulfide, 4-aminophenyl phenyl sulfide, 2-aminophenyl phenyl sulfone,3-aminophenyl phenyl sulfone, 4-aminophnyl phenyl sulfone,α-naphthylamine, β-naphthylamine, 1-amino-2-naphthol,2-amino-1-naphthol, 4-amino-1-naphthol, 5-amino-1-naphthol,5-amino-1-naphthol, 5-amino-2-naphthol, 7-amino-2-naphthol,8-amino-2-naphthol, 1-aminoanthracene, 2-aminoanthracene, and9-aminoanthracene. These monoamines may have a group unreactive withamines or dicarboxylic anhydrides in their molecules.

The end-capping agent is added in an amount of 20 parts by weight orless, preferably 1 to 10 parts by weight, more preferably 1 to 5 partsby weight, based on 100 parts by weight of the sum of thetetracarboxylic dianhydride and the diamine.

After the polymerization reaction, the resulting polyamic acid isimidized. Specifically, the imidization may be performed by chemicalimidization or thermal imidization. Thermal imidization is preferred.

Specifically, the chemical imidization may be performed using adehydrating agent. The dehydrating agent may be, for example, an acidanhydride, such as acetic anhydride, propionic anhydride or benzoicanhydride, or its acid chloride, or a carbodiimide compound, such asdicyclohexylcarbodiimide. The dehydrating agent is preferably used in anamount of 0.1 to 10 moles per mole of the acid dianhydride. The chemicalimidization may also be effected in combination with heating at atemperature of 60 to 120° C.

The thermal imidization may be performed by heat treatment at atemperature of 80 to 400° C. As a result of dehydration, water isformed, which is more preferably removed by azeotropic distillation withbenzene, toluene or xylene.

The chemical or thermal imidization process may be carried out in thepresence of a base catalyst, such as pyridine, isoquinoline,trimethylamine, triethylamine, N,N-dimethylaminopyridine, imidazole,1-methylpiperidine or 1-methylpiperazine. The base catalyst may be usedin an amount of 0.1 to 5 moles per mole of the acid dianhydride.

During the imidization process, water is formed from H of the —CO—NH—group and OH of the —CO—OH group and leaves from the polyamic acidmolecule, giving the polyimide having a cyclic chemical structure(—CO—N—CO—).

The polyimide may be separated from the polymerization solvent and driedbefore use. The polyimide is separated by adding a poor solvent for thepolyimide to the polyimide solution to obtain a precipitate, which isthen subjected to a series of processes, such as filtration, washing,and drying. The poor solvent may be, for example, methanol or isopropylether. Thereafter, the polyimide may be re-dissolved in the same organicsolvent as that used in the polymerization reaction.

The polyimide has a number average molecular weight of 500 to 80,000g/mol. The modified polyimide has a number average molecular weight of500 to 80,000 g/mol, preferably 500 to 50,000 g/mol or 500 to 30,000g/mol. The ratio of the weight average molecular weight to the numberaverage molecular weight (Mw/Mn) of the modified polyimide is from 1 to3, preferably from 1 to 2.

If the polyimide and the modified polyimide have number averagemolecular weights lower than 500 g/mol, the mechanical properties offilms produced therefrom may deteriorate. Meanwhile, if the polyimideand the modified polyimide have number average molecular weights higherthan 80,000, their flowability may be so low that problems, such asnon-uniform coating, may arise during processing.

The polyimide may be in the form of an oligomer with a relatively lowmolecular weight. In this case, the polyimide possesses a number ofreactive sites capable of reacting with curable reactive groups and hasimproved transmittance and low yellowness index (YI) resulting from itslow molecular weight.

According to one embodiment of the present invention, the polyimide isdissolved in a solvent and reacts with the compound of Formula 2including a curable functional group at room temperature to 80° C. for 5to 30 hours, preferably for 10 to 30 hours, giving the modifiedpolyimide including the repeating unit of Formula 1. If the reactiontemperature is too high or the reaction time is excessively long, thepolyimide solution may be gelled, resulting in non-uniform coating.

Any solvent that can dissolve the polyimide may be used in the reactionof the polyimide and the compound of Formula 2. Examples of suchsolvents include, aprotic solvents, such as N-methylpyrrolidone (NMP),N-ethylpyrrolidone (NEP) gamma-butyrolactone (GBL), dimethylformamide(DMF), diethylformamide (DEF), dimethylacetamide (DMAc),diethylacetamide (DEAc), tetrahydrofuran (THF), and 2-butyl cellosolve,meta-cresol, phenol, and halogenated phenols.

The polyimide may react with the compound of Formula 2 in a ratio of 1:2to 1:8, preferably 1:2 to 1:6.

The modified polyimide is mixed with a photopolymerization or thermalpolymerization initiator and a solvent to prepare a curable resincomposition.

The solvent is not particularly limited so long as it can uniformlydissolve the initiator and the modified polyimide and at the same timeis chemically stable enough not to react with the other components ofthe composition. For example, the solvent may be an aprotic solvent,such as N-methylpyrrolidone (NMP), N-ethylpyrrolidone (NEP)gamma-butyrolactone (GBL), dimethylformamide (DMF), diethylformamide(DEF), dimethylacetamide (DMAc), diethylacetamide (DEAc),tetrahydrofuran (THF) or 2-butyl cellosolve, meta-cresol, phenol or ahalogenated phenol.

The photopolymerization initiator may be, for example, one that servesto initiate radical photocuring in an exposed portion of the resincomposition. The photopolymerization initiator may be any of those knownin the art and examples thereof include: benzoin compounds, such asbenzoin, benzoin methyl ether, benzoin ethyl ether, and alkyl ethersthereof; acetophenone compounds, acetophenone,2,2-dimethoxy-2-phenylacetophenone, 1,1-dichloroacetophenone, and4-(1-t-butyldioxy-1-methylethyl)acetophenone; anthraquinone compounds,such as 2-methylanthraquinone, 2-amylanthraquinone,2-t-butylanthraquinone, and 1-chloroanthraquinone; thioxanthonecompounds, such as 2,4-dimethylthioxanthone,2,4-diisopropylthioxanthone, and 2-chlorothioxanthone; ketal compounds,such as acetophenone dimethyl ketal and benzyl dimethyl ketal; andbenzophenone compounds, such as benzophenone,4-(1-t-butyldioxy-1-methylethyl)benzophenone, and3,3′,4,4′-tetrakis(t-butyl dioxycarbonyl)benzophenone.

α-aminoacetophenone compounds, such as2-methyl-1-[4-(methylthio)phenyl]-2-morpholinopropanone-1,2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)-butan-1-one,2-(dimethylamino)-2-[(4-methylphenyl)methyl]-1-[4-(4-morpholinyl)phenyl]-1-butanone,N,N-dimethylaminoacetophenone (Irgacure® 907, Irgacure® 369, andIrgacure® 379 available from Ciba Specialty Chemicals (now Ciba Japan),and acylphosphine oxide compounds, such as2,4,6-trimethylbenzoyldiphenylphosphine oxide,bis(2,4,6-trimethylbenzoyl)-phenylphosphine oxide, andbis(2,6-dimethoxybenzoyl)-2,4,4-trimethyl-pentylphosphine oxide (e.g.,Lucilin® TPO available from BASF and Irgacure® 819 available from CibaSpecialty Chemicals may also be used as suitable photoinitiators.

As other suitable photoinitiators, there may be mentioned oxime estercompounds. Specific examples of the oxime ester compounds include2-(acetyloxyiminomethyl)thioxanthen-9-one, (1,2-octanedione,1-[4-(phenylthio)phenyl]-, 2-(O-benzoyloxime)), (ethanone,1-[9-ethyl-6-(2-methylbenzoyl)-9H-carbazol-3-yl]-, 1-(0-acetyloxime)).Examples of commercially available products for these oxime estercompounds include GGI-325, Irgacure OXE01 and Irgacure OXE02 from CibaSpecialty Chemicals, N-1919 from ADEKA, and Darocur TPO from CibaSpecialty Chemicals. In addition to these, biimidazole compounds andtriazine compounds may also be used as photoinitiators.

The photopolymerization initiator may be present in an amount of about0.5 to about 20% by weight, about 1 to about 10% by weight or about 1 toabout 5% by weight, based on the total weight of the resin composition.If the content of the photoinitiator is less than the lower limitdefined above, sufficient photocuring may not occur.

As the thermal polymerization initiator, there may be used any generalradical polymerization initiator known in the art. Examples of suchradical polymerization initiators include: azo compounds, such as2,2′-azobisisobutyronitrile, 2,2′-azobis(2,4-dimethylvaleronitrile), and2,2′-azobis(4-methoxy-2,4-dimethylvaleronitrile); organic peroxides,such as benzoyl peroxide, t-butyl peroxypivalate, and1,1′-bis-(t-butylperoxy)cyclohexane; and hydrogen peroxide. When aperoxide is used as a radical polymerization initiator, it can act as aredox initiator in combination with a reducing agent. The use of the azocompounds is preferred.

The thermal polymerization initiator is present in an amount of about0.5 to about 20% by weight, about 1 to about 15% by weight or about 5 toabout 10% by weight, based on the total weight of the resin composition.If the content of the photoinitiator is less than the lower limitdefined above, sufficient photocuring may not occur.

According to one embodiment, the curable resin composition may furtherinclude a polymerizable compound having an ethylenically unsaturatedbond and/or a urethane (meth)acrylate compound.

The polymerizable compound having an ethylenically unsaturated bond canimprove the heat resistance and surface hardness of a polyimideprotective film obtained in a subsequent step.

The polymerizable compound having an ethylenically unsaturated bond maybe selected from monofunctional, difunctional, trifunctional, and higherfunctional (meth)acrylates. Examples of the monofunctional(meth)acrylates include 2-hydroxyethyl (meth)acrylate, carbitol(meth)acrylate, isobornyl (meth)acrylate, 3-methoxybutyl (meth)acrylate,and 2-(meth)acryloyloxyethyl-2-hydroxypropyl phthalate.

Examples of the difunctional (meth)acrylates include ethylene glycol(meth)acrylate, 1,6-hexanediol (meth)acrylate, 1,9-nonanediol(meth)acrylate, propylene glycol (meth)acrylate, tetraethylene glycol(meth)acrylate, and bisphenoxy ethanol fluorene diacrylate.

Examples of the trifunctional and higher functional (meth)acrylatesinclude tris(hydroxyethyl)isocyanurate tri(meth)acrylate,trimethylolpropane tri(meth)acrylate, pentaerythritol tri(meth)acrylate,pentaerythritol tetra(meth)acrylate, and dipentaerythritolhexa(meth)acrylate.

These monofunctional, difunctional, trifunctional, and higher functional(meth)acrylates may be used alone or in combination of two or morethereof.

The polymerizable compound may be present in an amount of 20 to 100parts by weight, 20 to 70 parts by weight, preferably 20 to 50 parts byweight, based on 100 parts by weight of the modified polyimide ofFormula 4. If the content of the polymerizable compound is less than 20parts by weight, based on 100 parts by weight of the modified polyimide,the degree of curing of the modified polyimide cannot be improved.Meanwhile, if the content of the polymerizable compound exceeds 100parts by weight, the adhesiveness of a resulting coating film tends todeteriorate.

The urethane (meth)acrylate compound may be, for example, selected from:hydroxy(meth)acrylate compounds, such as hydroxymethyl (meth)acrylate,hydroxyethyl (meth)acrylate, and tetramethylolethane tri(meth)acrylate;and urethane (meth)acrylates containing an allophanate modifiedpolyisocyanurate. The urethane (meth)acrylate compound may be present inan amount of 20 to 100 parts by weight, 30 to 80 parts by weight,preferably 40 to 60 parts by weight, based on 100 parts by weight of themodified polyimide of Formula 4. If the content of the polymerizablecompound is less than 20 parts by weight, based on 100 parts by weightof the modified polyimide, the degree of curing of the modifiedpolyimide cannot be improved. Meanwhile, if the content of thepolymerizable compound exceeds 100 parts by weight, the adhesiveness ofa resulting coating film tends to deteriorate.

According to one embodiment, the urethane resin has a weight averagemolecular weight in the range of 1,000 to 20,000. Within this range, theviscosity of the composition can be controlled such that high processingefficiency is achieved.

The heat curable resin composition of the present invention may furtherinclude one or more additives selected from the group consisting ofsurfactants, adhesion aids, radical thermal polymerization initiators,and antioxidants.

The present invention will be explained in detail with reference to thefollowing examples, including comparative examples. These examples aremerely illustrative and the scope of the invention is not limitedthereto.

<Preparative Example 1> Modified TFMB-ODPA (1:1.1) PolyimidePolymerization (3 Mol MOI)

1 mol of 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB) wasdissolved in 80 g of diethylformamide (DEF), and 1.1 mol of4,4′-oxydiphthalic anhydride (ODPA) were added thereto. The mixture wasallowed to polymerize in 50 g of diethylformamide (DEF) at 50° C. for 24h to prepare a polyamic acid solution.

40 g of toluene was added to the solution and a Dean-Stark distillationapparatus was installed to remove water. The mixture was heated toreflux at 180° C. for 12 h. The resulting polyimide solution wasprecipitated with methanol. The precipitate was collected, dried, anddissolved in 50 g of DEF. The solution was added with 3 mol of2-methacryloyloxyethyl isocyanate (MOI) and 30 g of DEF. The mixture wasallowed to react at room temperature for 24 h, precipitated in methanol,and dried, affording a modified polyimide.

<Preparative Example 2> Modified TFMB-ODPA (1:1.3) PolyimidePolymerization (5 Mol MOI)

1 mol of 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB) wasdissolved in 80 g of diethylformamide (DEF), and 1.3 mol of4,4′-oxydiphthalic anhydride (ODPA) were added thereto. The mixture wasallowed to polymerize in 50 g of diethylformamide (DEF) at 50° C. for 24h to prepare a polyamic acid solution.

40 g of toluene was added to the solution and a Dean-Stark distillationapparatus was installed to remove water. The mixture was heated toreflux at 180° C. for 12 h. The resulting polyimide solution wasprecipitated with methanol. The precipitate was collected, dried, anddissolved in 50 g of DEF. The solution was added with 5 mol of2-methacryloyloxyethyl isocyanate (MOI) and 30 g of DEF. The mixture wasallowed to react at room temperature for 24 h, precipitated in methanol,and dried, affording a modified polyimide.

<Preparative Example 3> TFMB-ODPA (1:1) Polyimide Polymerization

1 mol of 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB) wasdissolved in 80 g of diethylformamide (DEF), and 1.1 mol of4,4′-oxydiphthalic anhydride (ODPA) were added thereto. The mixture wasallowed to polymerize in 50 g of diethylformamide (DEF) at 50° C. for 24h to prepare a polyamic acid solution.

40 g of toluene was added to the solution and a Dean-Stark distillationapparatus was installed to remove water. The mixture was heated toreflux at 180° C. for 12 h. The resulting polyimide solution wasprecipitated with methanol. The precipitate was collected and dried,affording a non-modified TFMB-ODPA polyimide.

<Preparative Example 4> TFMB-BPADA (1:1) Polyimide Polymerization

1 mol of 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB) wasdissolved in 80 g of diethylformamide (DEF), and 1 mol of2,2-bis[4-(2,3-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA) wereadded thereto. The mixture was allowed to polymerize in 80 g ofdiethylformamide (DEF) at 50° C. for 24 h to prepare a polyamic acidsolution.

50 g of toluene was added to the solution and a Dean-Stark distillationapparatus was installed to remove water. The mixture was heated toreflux at 160° C. for 12 h. The resulting polyimide solution wasprecipitated with methanol. The precipitate was collected and dried,affording a non-modified TFMB-BPADA polyimide.

<Preparative Example 5> TFMB-BPADA (1:1.1) Polyimide Polymerization

1 mol of 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB) wasdissolved in 80 g of diethylformamide (DEF), and 1.1 mol of2,2-bis[4-(2,3-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA) wereadded thereto. The mixture was allowed to polymerize in 80 g ofdiethylformamide (DEF) at 50° C. for 24 h to prepare a polyamic acidsolution.

50 g of toluene was added to the solution and a Dean-Stark distillationapparatus was installed to remove water. The mixture was heated toreflux at 160° C. for 12 h. The resulting polyimide solution wasprecipitated with methanol. The precipitate was collected and dried,affording a non-modified TFMB-BPADA polyimide.

<Preparative Example 6> TFMB-BPADA (1:1.3) Polyimide Polymerization

1 mol of 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB) wasdissolved in 80 g of diethylformamide (DEF), and 1.3 mol of2,2-bis[4-(2,3-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA) wereadded thereto. The mixture was allowed to polymerize in 80 g ofdiethylformamide (DEF) at 50° C. for 24 h to prepare a polyamic acidsolution.

50 g of toluene was added to the solution and a Dean-Stark distillationapparatus was installed to remove water. The mixture was heated toreflux at 160° C. for 12 h. The resulting polyimide solution wasprecipitated with methanol. The precipitate was collected and dried,affording a non-modified TFMB-BPADA polyimide.

<Preparative Example 7> Modified TFMB-BPADA (1:1.1) PolyimidePolymerization (3 Mol MOI)—Room Temperature, 10 h

1 mol of 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB) wasdissolved in 80 g of diethylformamide (DEF), and 1.1 mol of2,2-bis[4-(2,3-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA) wereadded thereto. The mixture was allowed to polymerize in 80 g ofdiethylformamide (DEF) at 50° C. for 24 h to prepare a polyamic acidsolution.

50 g of toluene was added to the solution and a Dean-Stark distillationapparatus was installed to remove water. The mixture was heated toreflux at 160° C. for 12 h. The resulting polyimide solution wasprecipitated with methanol. The precipitate was collected, dried, anddissolved in 50 g of DEF. The solution was added with 3 mol of2-methacryloyloxyethyl isocyanate (MOI) and 30 g of DEF. The mixture wasallowed to react at room temperature for 10 h, precipitated in methanol,and dried, affording a modified polyimide.

<Preparative Example 8> Modified TFMB-BPADA (1:1.1) PolyimidePolymerization (3 Mol MOI)—Room Temperature, 10 h/50° C., 6 h

1 mol of 2,2′-bis(trifluoromethyl)-4,4′-diaminobiphenyl (TFMB) wasdissolved in 80 g of diethylformamide (DEF), and 1.1 mol of2,2-bis[4-(2,3-dicarboxyphenoxy)phenyl]propane dianhydride (BPADA) wereadded thereto. The mixture was allowed to polymerize in 80 g ofdiethylformamide (DEF) at 50° C. for 24 h to prepare a polyamic acidsolution.

50 g of toluene was added to the solution and a Dean-Stark distillationapparatus was installed to remove water. The mixture was heated toreflux at 160° C. for 12 h. The resulting polyimide solution wasprecipitated with methanol. The precipitate was collected, dried, anddissolved in 50 g of DEF. The solution was added with 3 mol of2-methacryloyloxyethyl isocyanate (MOI) and 30 g of DEF. The mixture wasallowed to react at room temperature for 10 h. The reaction mixture wasallowed to further react at 50° C. for 6 h, precipitated in methanol,and dried, affording a modified polyimide.

<Preparation of Heat Curable Coating Compositions>

Example 1

10 g of the modified polyimide prepared in Preparative Example 1 wasmixed with 1 g of 2,2′-azobis(2,4-dimethylvaleronitrile) (V65, WAKOCHEMICAL, 10 hour half-life temperature: 50° C.) as a thermalpolymerization initiator. To the mixture was added diethylformamide(DEF) in such an amount that the solid content was 30 wt %, giving aheat curable coating composition.

Example 2

3 g of dipentaerythritol hexaacrylate (DPHA) was added to 10 g of themodified polyimide prepared in Preparative Example 1, and then 1 g of2,2′-azobis(2,4-dimethylvaleronitrile) (V65, WAKO CHEMICAL, 10 hourhalf-life temperature: 50° C.) as a thermal polymerization initiator wasadded thereto. To the mixture was added diethylformamide (DEF) in suchan amount that the solid content was 30 wt %, giving a heat curablecoating composition.

Example 3

5 g of a urethane acrylic oligomer (SP260, SOLTECH LTD.) and 4 g ofdipentaerythritol hexaacrylate (DPHA) were sequentially added to 10 g ofthe modified polyimide prepared in Preparative Example 1, and then 1 gof 2,2′-azobis(2,4-dimethylvaleronitrile) (V65, WAKO CHEMICAL, 10 hourhalf-life temperature: 50° C.) as a thermal polymerization initiator wasadded thereto. To the mixture was added diethylformamide (DEF) in suchan amount that the solid content was 30 wt %, giving a heat curablecoating composition.

Example 4

5 g of a urethane acrylic oligomer (SU5260, SOLTECH LTD.) and 4 g ofdipentaerythritol hexaacrylate (DPHA) were sequentially added to 10 g ofthe modified polyimide prepared in Preparative Example 1, and then 1 gof 2,2′-azobis(2,4-dimethylvaleronitrile) (V65, WAKO CHEMICAL, 10 hourhalf-life temperature: 50° C.) as a thermal polymerization initiator wasadded thereto. To the mixture was added diethylformamide (DEF) in suchan amount that the solid content was 30 wt %, giving a heat curablecoating composition.

Comparative Example 1

5 g of a urethane acrylic oligomer (SU594, SOLTECH LTD.) and 4 g ofdipentaerythritol hexaacrylate (DPHA) were sequentially added to 10 g ofthe polyimide prepared in Preparative Example 3, and then 1 g of2,2′-azobis(2,4-dimethylvaleronitrile) (V65, WAKO CHEMICAL, 10 hourhalf-life temperature: 50° C.) as a thermal polymerization initiator wasadded thereto. To the mixture was added diethylformamide (DEF) in suchan amount that the solid content was 30 wt %, giving a heat curablecoating composition.

Comparative Example 2

10 g of the polyimide prepared in Preparative Example 3 was mixed with 1g of 2,2′-azobis(2,4-dimethylvaleronitrile) (V65, WAKO CHEMICAL, 10 hourhalf-life temperature: 50° C.) as a thermal polymerization initiator. Tothe mixture was added diethylformamide (DEF) in such an amount that thesolid content was 30 wt %, giving a heat curable coating composition.

EXPERIMENTAL EXAMPLES <Experimental Example 1> Measurement of OpticalProperties of Coating Films

Each of the heat curable coating compositions prepared in Examples 1-4and Comparative Examples 1-2 was spin coated on a 50 μm thick glasssubstrate. The coated substrate was heated to 250° C. at a rate of 3°C./min in an oven under a nitrogen atmosphere. After heating foradditional 60 min, a ˜21 μm thick monolayer polymer film was peeled fromthe substrate.

The polyimide films were measured for optical properties, includingtransmittance, yellowness index, retardation value, and coefficient ofthermal expansion by the following procedures. The results are shown inTable 1.

Transmittance was measured using a transmittance meter (HR-100, MurakamiColor Research Laboratory) in accordance with JIS K 7105.

Yellowness index (YI) was measured using a colorimeter [Colorimeter](Color Eye 7000A).

The thickness retardation (Rth) of each film was measured using Axoscan.First, the film was cut to a predetermined size and the thickness of thesample was measured. The retardation of the sample was measured usingAxoscan and the measured thickness was input while calibrating in theC-plate direction to compensate for the retardation value. Therefractive index of the sample was measured by inputting the refractiveindex of the polyimide.

TABLE 1 Comparative Comparative Example 1 Example 2 Example 1 Example 2Example 3 Example 4 Thickness mm 21 21 21 21 21 21 UV 550 nm % 10 87.688.7 90 90 90 transmittance 460 nm % 2 73 84 86 88 88 Cut off nm 450 368361 361 355 355 Haze % 1.0 70 0.8 0.8 0.4 0.3 Y.I — 10 19 6.0 4.7 2.22.2 R_(th) nm 500 120 154 154 56 53 [(n_(x) + n_(y))/2 − n_(z)]d T_(g) °C. 280 — 255 225 240 260

<Experimental Example 2> Confirmation of Synthesis of the ModifiedPolyimides

<Attenuated Total Reflectance (ATR) Measurement>

The ATR peaks of the modified polyimides prepared in PreparativeExamples 1-2 were compared with those of the polyimide prepared inPreparative Example 3 to confirm the presence of acrylate groups in themodified polyimides. The results are shown in FIGS. 1 and 2.

FIG. 1 shows ATR spectra of the acrylate modified TFMB-ODPA polyimideprepared in Preparative Example 2 (1a) and the TFMB-ODPA polyimideprepared in Preparative Example 3 (1 b). The peaks of the TFMB-ODPApolyimide (1b) were subtracted from the peaks of the modified polyimide(1a). The remaining peaks ((c) of FIG. 1) indicate the presence ofacrylate groups bonded to the modified TFMB-ODPA polyimide ofPreparative Example 2.

<Measurement of HMBC NMR (¹H-¹³C) and COSY NMR (¹H-¹H)>

HMBC NMR (¹H-¹³C) and COSY NMR (¹H-¹H) spectra were recorded on anAVENCE III HD 700 MHz NMR spectrometer. Chemical shifts are reported inppm relative to the peak of trimethylsilane (TMS) at 0 ppm.

HMBC NMR (¹H-¹³C) and COSY NMR (¹H-¹H) spectra of the modified polyimideprepared in Preparative Example 8 are shown in FIG. 3. The proton peaksat 4-4.5 ppm in FIG. 3 reveal the presence of —NCH₂ of the polyimiderings formed due to the reaction of the terminal groups of the polyimidewith the isocyanate. The proton peaks of OCH₂ adjacent to C═O of theimide rings and C═O of the acrylic groups were observed at 5.5 ppm and4.4 ppm, respectively. The proton peaks of CH₂═C corresponding to thedouble bonds of the acrylic groups could be found between 5.5 ppm and 6ppm.

<Experimental Example 3> Molecular Weight Measurement

<Measurement of Number Average Molecular Weight Using ¹³C-NMR>

¹³C-NMR spectra of the polyimides prepared in Preparative Examples 4-6were measured. The number average molecular weight of each modifiedpolyimide was determined by comparing the integral value of CF₃ peak wascompared with that of (COO)₂O peak of the terminal acid dianhydridegroups.

¹³C-NMR spectra were recorded on an AVENCE III HD 700 MHz NMRspectrometer. Chemical shifts are reported in ppm relative to the peakof trimethylsilane (TMS) at 0 ppm.

The measured molecular weights and PDI values are shown in Table 2.

<Measurement of Number Average Molecular Weight and Weight AverageMolecular Weight Using Gel Permeation Chromatography (GPC)>

The number average molecular weight and weight average molecular weightof each of the polyimides prepared in Preparative Examples 4-6 weremeasured using gel permeation chromatography (GPC) to determine the PDIvalue of the polyimide. For GPC measurement, a mixture of THF and DMF(50:50, v/v) was used as the eluent.

The results are shown in Table 2.

TABLE 2 Mn by Mol ratio Mn by ¹³C-NMR^(a) GPC PDI by BPADA TFMB (g/mol)(g/mol) GPC^(b) Preparative 1.0 1.0 — 24,500 2.06 Example 4 Preparative1.1 1.0 9700 8811 1.77 Example 5 Preparative 1.3 1.0 4591 5211 1.28Example 6 ^(a))CF₃:—(COO)₂O ^(b))PDI = M_(w)/M_(n)

<Experimental Example 4> Measurement of Imidization Ratio Using ¹H-NMR

¹H-NMR spectra of the polyimides prepared in Preparative Examples 1, 2,5, and 6 were measured and are shown in FIG. 4. In each ¹H-NMR spectrum,the proton of the structure remaining unchanged before and afterimidization was defined as the standard proton, and the integral valueof the peak of the standard proton and the integral value of the peakcorresponding to the proton of the NH group of the amide moiety found ataround 10-11 ppm were used to calculate the imidization ratio of thepolyimide.

¹H-NMR spectra were recorded on an AVENCE III HD 700 MHz NMRspectrometer. Chemical shifts are reported in ppm relative to the peakof trimethylsilane (TMS) at 0 ppm.

As shown in FIG. 4, the acrylic modified polyimides prepared inPreparative Examples 1-2 showed high imidization ratios and were foundto have high peaks corresponding to the proton of CONK However, nosubstantial peak corresponding to the proton of COOH was observed. Thisprovides a basis for the presence of the repeating structure of Formula5 or 6 in the main chains of the polyimides of Examples 1 and 2.

<Experimental Example 5> Evaluation of Reactivity Depending on ReactionTemperature

The polyimide prepared in Preparative Example 5 was dissolved in 50 g ofDEF, and 3 mol of 2-methacryloyloxyethyl isocyanate (MOI) and 30 g ofDEF were sequentially added thereto. The mixture was allowed to react atvarious temperatures (room temperature, 50° C., 80° C., and 100° C.) for10 h. The states of the reaction solution were observed.

The polyimide prepared in Preparative Example 6 was dissolved in 50 g ofDEF, and 5 mol of 2-methacryloyloxyethyl isocyanate (MOI) and 30 g ofDEF were sequentially added thereto. The mixture was allowed to react atvarious temperatures (room temperature, 50° C., 80° C., and 100° C.) for10 h. The states of the reaction solutions were observed.

The results are shown in Table 3.

TABLE 3 Temperature BPADA_TFMB (° C.) Preparative Example 5 PreparativeExample 6 r.t Homogeneous Homogeneous 50 Homogeneous Homogeneous 80Gelation Gelation 100  Gelation Gelation

<Experimental Example 6> Evaluation of Reactivity Depending on ReactionTemperature and Time

¹H-NMR spectra of the modified polyimides prepared in PreparativeExamples 5, 7, and 8 were measured and are shown in FIG. 5. Changes inthe reactivity of the isocyanate depending on temperature and time wereevaluated by calculating the ratios of the integral values of the protonpeaks of the acrylate-related CH₂═C, OCH₂, and NCH₂ to the integralvalue of the Ar—H proton of each modified polyimide.

As shown in FIG. 5, the intensities of the acrylate-related proton peaksin the spectrum of the modified polyimide of Preparative Example 8 wereon average 2 times larger than those in the spectrum of the modifiedpolyimide of Preparative Example 7. The modified polyimide ofPreparative Example 7 was prepared by reacting the polyimide with theisocyanate at room temperature for 10 h, whereas the modified polyimideof Preparative Example 7 was prepared by reacting the polyimide with theisocyanate at room temperature for 10 h and at 50° C. for additional 6h. The increased peak intensities demonstrate that a larger number ofacrylate groups were bonded to the main chain of the polyimide of thePreparative Example 8 by the reaction of the polyimide and theisocyanate. These results lead to the conclusion that the number of thecurable functional groups introduced into the polyimide can becontrolled by optimizing the reaction temperature and time conditions.

1. A modified polyimide comprising a terminal group represented byFormula 1:

wherein D is a heat curable or photocurable functional group, R is adivalent or higher polyvalent organic group, and n is an integer of 1 orgreater.
 2. The modified polyimide according to claim 1, wherein theterminal group of Formula 1 is derived from the reaction of a terminalacid dianhydride group of a polyimide and a compound of Formula 2:

wherein R, D, and n are as defined in Formula
 1. 3. The modifiedpolyimide according to claim 1, wherein the modified polyimide isrepresented by Formula 4:

wherein X₁, X₂, X₃, and X₄ are each independently a tetravalent organicgroup derived from a tetracarboxylic dianhydride, Y₁, Y₂, and Y₃ areeach independently a divalent organic group derived from a diamine, p,q, r, and v are each independently an integer of 0 or greater, with theproviso that p, q, r, and v are not simultaneously 0, and D, R, and nare as defined in Formula
 1. 4. The modified polyimide according toclaim 3, further comprising, in its main chain, one or more repeatingstructures represented by Formulae 5a to 5c:

wherein R_(a) and R_(b) are each independently selected from the groupconsisting of aromatic, alicyclic, and aliphatic divalent organicgroups,

wherein R_(c) and R_(d) are each independently selected from the groupconsisting of aromatic, alicyclic, and aliphatic divalent organicgroups, and

wherein R_(e) and R_(f) are each independently selected from the groupconsisting of aromatic, alicyclic, and aliphatic divalent organicgroups.
 5. The modified polyimide according to claim 1, wherein D inFormula 1 is selected from the group consisting of vinyl, alkyne,acrylate, carboxyl, amide, amino, epoxy, isocyanate, cyano, acidanhydride, mercapto, silanol, alkoxysilane, hydroxyl, oxazoline groups,and combinations thereof.
 6. The modified polyimide according to claim1, wherein D in Formula 1 is selected from acrylate, epoxy, isocyanate,mercapto groups, and combinations thereof.
 7. The modified polyimideaccording to claim 3, wherein in Formula 4, X₁, X₂, X₃, and X₄ are eachindependently a tetravalent organic group derived from an aromatictetracarboxylic dianhydride and Y₁, Y₂, and Y₃ are each independently adivalent organic group derived from an aromatic diamine.
 8. The modifiedpolyimide according to claim 3, wherein the modified polyimide ofFormula 4 is prepared by reacting a polyimide compound represented byFormula 3:

wherein X₁, X₂, X₃, and X₄ are each independently a tetravalent organicgroup derived from a tetracarboxylic dianhydride, Y₁, Y₂, and Y₃ areeach independently a divalent organic group derived from a diamine, andw and z are each independently an integer of 1 or greater, with anisocyanate compound represented by Formula 2:

wherein D, R, and n are as defined in Formula
 4. 9. The modifiedpolyimide according to claim 1, wherein modified polyimide has a numberaverage molecular weight of 500 to 80,000 g/mol.
 10. The modifiedpolyimide according to claim 3, wherein in Formula 4, the sum of p+q+r+vis an integer from 5 to
 100. 11. The modified polyimide according toclaim 1, wherein the ratio of the weight average molecular weight to thenumber average molecular weight of the modified polyimide is 1 orgreater.
 12. The modified polyimide according to claim 2, wherein thecompound of Formula 2 is a compound represented by Formula 2a:

wherein R₁ is a C₁-C₁₈ alkylene group, a C₆-C₂₄ arylene group or adivalent organic group interrupted by at least one ether, ester,urethane or amide bond as a linker, and R₂ is a hydrogen atom or aC₁-C₁₈ alkyl group.
 13. The modified polyimide according to claim 8,wherein the polyimide of Formula 3 is prepared by reacting thetetracarboxylic dianhydride with the diamine in a molar ratio of 1:1 to1.8:1.
 14. A curable resin composition comprising the modified polyimideaccording to claim 1, a thermal polymerization or photopolymerizationinitiator, and a solvent.
 15. The curable resin composition according toclaim 14, wherein the solvent is selected from N,N-diethylacetamide(DEAc), N,N-diethylformamide (DEF), N-ethylpyrrolidone, and mixturesthereof.
 16. The curable resin composition according to claim 14,further comprising a polymerizable compound having an ethylenicallyunsaturated bond, a urethane (meth)acrylate compound or a mixturethereof.
 17. A polyimide film obtained by curing the curable resincomposition according to claim
 14. 18. The polyimide film according toclaim 17, wherein the polyimide film has a yellowness index (YI) of 7 orless, as measured at a thickness of 10 μm or more.
 19. A method forpreparing a modified polyimide having terminal curable functionalgroups, represented by Formula 4:

wherein X₁, X₂, X₃, and X₄ are each independently a tetravalent organicgroup derived from a tetracarboxylic dianhydride, Y₁, Y₂, and Y₃ areeach independently a divalent organic group derived from a diamine, p,q, r, and v are each independently an integer of 0 or greater, with theproviso that p, q, r, and v are not simultaneously 0, D is a heatcurable or photocurable functional group, R is a divalent or higherpolyvalent organic group, and n is an integer of 1 or greater, themethod comprising reacting the tetracarboxylic dianhydride with thediamine in a polymerization solvent to prepare a polyamic acid,imidizing the polyamic acid to prepare a polyimide having terminal aciddianhydride groups, represented by Formula 3:

wherein X₁, X₂, X₃, X₄, Y₁, Y₂, and Y₃ are as defined in Formula 4 and wand z are each independently an integer of 1 or greater, and reactingthe polyimide of Formula 3 with a compound represented by Formula 2:O═C═N—RD]_(n)  (2) wherein D, R, and n are as defined in Formula
 4. 20.The method according to claim 19, wherein the polymerization solvent isselected from N,N-diethylacetamide (DEAc), N,N-diethylformamide (DEF),N-ethylpyrrolidone, and mixtures thereof.